The US administration and the defence department have ordered their employees not to read the secret diplomatic cables and other classified documents leaked by WikiLeaks and published by other media.

The US administration and the defence department have ordered their employees not to read the secret diplomatic cables and other classified documents leaked by WikiLeaks and published by other media.

Hundreds of thousands of federal employees as well as contractors have been asked not to read the secret documents unless they have the required security clearance or authorisation, the New York Times reported on Sunday.

"Classified information, whether or not already posted on public websites or disclosed to the media, remains classified, and must be treated as such by federal employees and contractors, until it is declassified by an appropriate US government authority," said the notice sent Friday by the the White House, to agency and department heads, urging them to distribute it to their staff.

The directive applies to both government computers and private devices that employees or contractors might carry in their briefcases and pockets or have in their homes.

However, it does not advise agencies to block WikiLeaks or other websites on government computer systems, a White House official said Saturday. And it does not prohibit federal employees from reading news stories about the topic. But if they have "accidentially" already downloaded any of these documents, they are being told to notify their "information security offices".

The US defence department, in its own directive to military personnel and contractors, has said reading these documents without proper authorisation will violate long-standing rules even though they are accessible to the public through internet.

"Viewing or downloading still classified documents from unclassified government computers creates a security violation," a spokeswoman said in a statement on Saturday.

The Library of Congress has also blocked visitors to its reading rooms, or anyone else using its computer system, from accessing the WikiLeaks site, noting that "unauthorised disclosures of classified documents do not alter the documents' classified status or automatically result in declassification of the documents."

WikiLeaks posted Twitter feeds mocking the efforts to limit access to the documents.

"Digital McCarthyism: US Military Tries to Intimidate Soldiers Into Not Reading Wikileaks," read a post on Saturday.